Sue Wheat thought a wood-burning stove was the greenest way to heat her house until a chat with authors, Nick Grant and Alan Clarke, made her think again. The biggest crisis of her eco-refurb so far? You bet it was!

With the cold weather closing in, it was time to think about green ways to heat our home. We chose a Stovax multi-fuel stove, which we were lucky enough to get from friends.

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In a city where every other house seems to be having its kitchen or bathroom ripped out, there is vast amounts of burnable scrap wood lying around waiting to go to the dump, which could instead be heating your house. Paying for wood to burn seems positively stupid when you can pick up a week’s supply from neighbours, most of whom are all too willing to let you have it. I can’t see the logic in buying wood that’s been transported hundreds of miles either, so I’ve become something of an eagle-eyed wood-spotting obsessive. We look for wood that’s unvarnished, unpainted and untreated, and either carry it home, or rope in friends with cars or vans to pick it up for us. I’ve also got a few friendly builders who drop off scrap wood to us (thus saving them dumping fees), and a supply of off-cuts from a furniture repair workshop. To build up next year’s wood store, which we made from scrap wooden pallets covered with tarpaulin, we’re planning to buy some logs from a local tree surgeon and season them for a year, by which time the excitement of dragging wood out of skips and yards may well have worn off.

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As I basked rather smugly in the warm glow of our pretty, near zero-carbon heating system, for a good few weeks I was unaware that things were about to get tricky. Then with one click on the mouse, I stumbled across a website which catapulted me into my biggest eco-refurbishment crisis yet. It seems, according to some of the eminent researchers at the Association of Environmentally Conscious Builders [AECB] that burning wood is not carbon neutral after all. I was gutted, to say the least. I emailed the AECB in a panic, who put me onto the authors of Biomass: A Burning Issue, Nick Grant and Alan Clarke. Their paper concludes that while it’s true that trees do absorb carbon dioxide when they grow, it doesn’t mean that the best use for the wood biomass is burning it. Burning, say Grant and Clarke, produces more carbon emissions than burning gas. Disaster.

Instead, they argue that timber should be left unburnt, thus imprisoning the carbon, and put to other uses; for example, as structural timber, insulation material or furniture. As owners of low-energy houses fuelled by wood burning stoves, they are both gutted too. ‘We don’t want people to hate us,’ Nick told me. ‘Please don’t shoot the messenger.’ The unfortunate result of assuming that wood-burning is carbon neutral is that it has been promoted by just about everyone, which has meant, as they point out, that wood is now being burnt faster than it’s grown, leading to rising prices and unsustainable burning practices to start.

4 Responses to “Burning Wood: Not So Carbon Neutral?”

Amongst other problems in the original article, from Figure 1 the authors don’t appear to understand that when you convert trees into timber products you generate waste. This waste will rot and generate CO2. If this waste is used for heating it can displace the use of fossil fuels and reduce overall emissions.

Sensible environmental policy recognises the use of wood waste streams to generate low carbon, renewable energy. That’s why governments in NZ, Australia, Northern America and across Europe are all encouraging wood energy systems. Austria, for example, has very ambitious greenhouse reduction targets and sees biomass as a key contributor to this goal.

So I think Sue can rest assured that as long as her wood fueled heater is a modern, efficient model and is fueled by waste wood she is making a positive contribution to emissions reduction.

For the same reason, the Wilderness Society is right now mounting a campaign against the increasing practice of burning forest trees in ‘biomass’ power plants to produce electricity.

One example is the burning of camphor laurels, a rampant weed tree in northern NSW, in plants to power sugar mills; the trees should be cut and replaced by natives, but used for timber or left to rot, not burned.

The trouble with the original paper is that it assumes that there is some alternitive way to forever sequester the carbon in the wood that is being burned. In most cases that is not a true assumption. In the most relevant case, in western North America, there are huge swaths of timber that are dying because of beetle kill. Most of this lumber is going unharvested to either decompose or burn in wildfire, which will eventually release its carbon without offseting any home heating needs. This timber has virtually no commercial value and there is no means to bury it underground to prevent its carbon release. Even in the illistrated case, there is no practical means to leave unburnt or undecomposed the sort of scrap wood that Sue Wheat is using. Even if some of this scrap wood could be used in furniture or housing, eventually it too will release its carbon in a landfill when the house is torn down or the furniture thrown out. In a steady state system (sustainable) it slows the burning of truly sequestered fuel that today lies deep underground.

Measuring carbon-only pollution is another terrible mistake when it comes to being green. Not only are there worse GHGs (methane!) there is also the problem of massive plant and equipment intrusions (involved in gas) destroying or at least badly polluting those areas. I think on balance, unless you’re looking at a bio-digestor for compost-based heating or bio-gas cooking (some combination), you’re looking at a less-than-ideal solution. But factor into those solutions remodeling your house? Is that still green? Not to mention regulations on such things (great to hear if anyone has experience here!). So while burning sensibly sourced (already dead, abandoned) wood might not be fantastic, it’s almost certain to be better than: * coal (can release as much radioactive thorium and uranium in power generation plant is considered unsafe by a nuclear variety plant!) * coal gas (see ‘gasland’) * fossil generated natural gases (liberating fossil gas, long since locked up, rather than catching gas already ‘in the system’)

If the fire is modern and is low emission, chances are it will clean up the nasty things used (mineral turpentine, etc) to season some ex-construction woods too, although I wouldn’t recommend using that stuff in the first place unless it’s been through some sort of seller who vets / measures potential emissions / toxins in said woods. Any amount of evil yick can be in it.

If you grow your own (wood or elephant grass, if legal in your area) you can be relatively certain (at least carbon-wise) your emissions are only what you put into your fuel stock when growing it in the first place.